Sozer, E. M., Stojanovic, M., and Proakis, J. G., “Underwater acoustic networks”, IEEE Journal of Oceanic Engineering, Vol. 25, No. 1, January 2000, 72-83 (hereinafter, abbreviated as Sozer) discloses an underwater communication network system, which includes plural underwater acoustic communication devices and a base station. FIG. 10 shows an example of a schematic configuration of the underwater communication network system. The underwater communication network system in FIG. 10 includes underwater acoustic communication devices (hereinafter, referred to as underwater terminals) T11 and T12 installed in the sea 10 or at bottom of the sea, and a base station B11 connected to a backbone network 20 installed in the sea 10. An acoustic communication method is adopted to data communication between the underwater terminals T11 and T12, between the underwater terminal T11 and the base station B11, and between the underwater terminal T12 and the base station B11.
A wired underwater communication system is also known. FIG. 11 shows an example of the wired underwater communication system, where all underwater terminals T21 and T22 are connected to a base station B21 through cables 11 and 12, respectively.